This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-24275 filed Feb. 1, 2000.
The present invention relates to an engine control unit, and particularly to an engine control unit which controls an internal combustion engine by switching frequencies of rotation pulses based on engine operation conditions.
An engine control unit (ECU) is an electronic control unit for performing controls such as fuel injection control, ignition control, and idle speed control to operate an engine in an optimum state. Specifically, signals from various sensors for sensing engine operating states such as crank angle sensor and engine coolant temperature sensor are supplied to the ECU to control an optimum fuel injection amount, injection timing, ignition timing, and the like.
Controls synchronized with the engine speed such as ignition control and injection control, that is, controls synchronized with a crankshaft rotation position, are performed by generating a signal of ignition pulses or the like after elapse of offset (delay) time from a predetermined crankshaft rotation position indicated by the edge of a crank signal.
It is, however, necessary to perform an arithmetic operation for converting the angle to time. There is a demand for reduction in processing load and improvement in accuracy. Further, it is desired to provide ignition sparks immediately after starting engine operation.
It is therefore an object of the present invention to provide an engine control unit with reduced processing load and improved accuracy and, moreover, capable of effecting ignition immediately after starting engine operation.
According to the present invention, a pulse interval in a crank signal having a pulse missing portion is measured. On the basis of the measured pulse interval, frequency multiplication signals of an integral multiple are generated by the next pulse. At the time of engine start, at least until the pulse missing portion in the crank signal is detected, the engine control is performed in accordance with a cam signal specifying a cylinder position and the crank signal so that ignition can be effected immediately after starting engine operation. At predetermined timing after the pulse missing portion in the crank signal is detected, the engine control is switched to use the frequency multiplication signals while performing initialization at the pulse missing portion in the crank signal.